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  <script>
    // `arr.includes(item, from)` 
    // item: 指 要找寻的元素 ,form 是开始索引(开始找寻的位置)
    // — 从索引 `from` 开始搜索 `item`，如果找到则返回 `true`（如果没找到，则返回 `false`）
    var arr = ["a", "b", "c", "d", "e", "d", "c"];
    console.log(arr.includes('f',0)); // false
    console.log(arr.includes('f')); // false 搜索区间不指定,默认是全部元素
    console.log(arr.includes('d')); // true

  </script>
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